Wearable electronic devices have gained popularity among consumers. A wearable electronic device may track user's activities using a variety of sensors and help the user to maintain a healthy life style. In order to determine a user's activities, a wearable electronic device collects activity data and runs computations on that data. One difficulty of obtaining accurate determinations of a user's activities is that these wearable electronic devices, because they are worn by a user, are typically packaged in a compact casing containing less powerful processor(s) (on which it is harder to run complex computations) than larger electronic devices.
Many wearable electronic devices may track metrics related to particular activities, such as a step count metric for running and walking activities. Other metrics that may be tracked by a wearable electronic device include metrics related to sleep. Typically, to initiate tracking of sleep metrics, a wearable electronic device may contain an interface for the user to provide notification that the user plans on transitioning into the asleep state (e.g., through the user pushing a button of or tap on the wearable electronic device).